The present invention relates to on-road comer dynamic balancing, and more particularly, the present invention relates to on-road comer dynamic balancing of vehicle wheels to reduce periodic vibrations occurring on a moving vehicle.
Vibrations are a common problem in conventional motor vehicles. The causes of these vibrations are numerous. Unwanted vibrations can arise from external excitations, such as those experienced while travelling over irregular road surfaces. Vibrations also arise from internal excitations, such as those caused by irregularities of internal moving parts, including the engine and wheels. These latter vibrations are periodic since their pattern recurs for every rotation of the respective component. The periodic vibrations exist due to the fact that it is impossible to manufacture perfectly uniform moving parts. For instance, during tire manufacturing verifications in tire thickness around the tire circumference can create thicker and thinner regions. This irregular thickness variation can result in a condition commonly known as runout observable through changes in the outside radius of the tire around the circumference. It can also manifest itself in localized weight variation as the mass is unevenly distributed around the tire circumference. This most commonly requires a conventional balance correction.
Another cause of vibration results from the tire bead being improperly manufactured or applied to the tire rim. Not only can this shift the tire mass distribution around the rim, but this can also yield a variation in runout thereby resulting in vibration.
A further source of vibration results from incorrect piloting or inherent piloting errors. Piloting is the means for achieving concentric registration of parts on a common rotary shaft. Its purpose is to perfectly align the centers of rotary parts with that of the shaft. Various implementations of piloting means are possible and indeed used for attaching vehicle wheels to the vehicle hubs, and they vary from product to product. Although the intention of the piloting means is perfect registration of the rotary parts, piloting on vehicles is inherently inaccurate, since the wheel is commonly positioned over the hub in a slip fit fashion. Lug bolts typically pass from the hub, through apertures in the wheel, to secure the wheel to the hub. The slip fit between the hub and the wheel, at interfaces that are designed to align the respective parts, allows the wheel to move radially with respect to the hub, resulting in an eccentric condition of attachment. This allows the wheel to radially shift and produces uneven runout and mass distributions from the center of rotation.
Many other causes of vehicle vibration exist. The above description is merely an overview. However, many of these vibration sources generate first order vibrations throughout the vehicle. First order vibrations are those that exist at frequencies identical to the rotational frequencies of the many shafts. Depending on the speed at which the vehicle is traveling and thus at what rotational speeds the wheels are turning, first order vibrations are transmitted throughout the vehicle at frequencies corresponding to the rotational speeds of the wheels. For instance, if the vehicle wheel is rotating at two complete revolutions per second, the frequency at which the first order vibration occurs throughout the vehicle is 2 hertz. Moreover, as vehicles usually contain a number of wheels, each tire excites its respective first order vibration through the vehicle, thereby resulting in a number of first order vibrations in the vehicle.
The vehicle wheels also generate other order vibrations, known as multi-order vibrations. However, these multi-order vibrations, occurring at frequencies corresponding to integer multiples of the rotational frequency in excess of unity, are typically less pronounced than those at first order frequencies. This situation is more clearly illustrated in FIG. 1. Here, the frequency order is listed on the X-Axis while its intensity is listed on the Y-axis. As shown, a first order frequency commonly has a large amplitude as compared with second, third, and fourth order frequencies, which diminish with respect to the order number. As can be seen, frequencies occurring at or near the first order frequencies typically account for the predominant vibrations occurring in a vehicle.
The vibrations excited by the vehicle wheels, whether first order or multi-order vibrations, are transmitted throughout the vehicle. These transmitted vibrations, in turn, result in portions of the vehicle, including portions located near the vehicle driver to occasionally vibrate excessively. When a system""s natural frequency, as shown in FIG. 2, overlaps with a frequency of an excitation the system oscillates at an exceptionally large amplitude. The vehicle is such a dynamic system and responds to the excitation at the wheels in this manner. At certain frequencies, therefore, the resulting vehicle vibrations can be readily noticed by a vehicle occupant. As the first order frequency generates the largest vibrations, it is usually the source of noticeable vibrations.
Manufacturers and service departments routinely attempt to reduce first order vibrations to eliminate these noticeable vibrations. Conventionally, the wheels and tires are xe2x80x9cbalancedxe2x80x9d as assemblies on shop floor machines to reduce contributions to the first order excitation. Alternatively, the vehicle is lifted from the floor of the service garage, and the wheels are xe2x80x9cbalancedxe2x80x9d while still affixed to the vehicle in order to reduce first order vibrations. This latter method is commonly referred to as xe2x80x9cOn-Car Balancingxe2x80x9d and employs special measurement transducers and analyzers. It also requires two measurement steps at each corner of the vehicle. During the initial measurement step of this method, a wheel is rotated independent of the remaining wheels to generate a first measurement indicative of the first order vibration on that particular wheel. A weight of known magnitude is then applied to a known location on the wheel and a second measurement is obtained. By using these two separate measurements, a weight and location can be determined which, when applied to the wheel, will offset and reduce the first order vibration. This procedure is repeated for each wheel independently to reduce the first order vibrations generated by the vehicle wheels. These balancing methods are well known to those skilled in the art and are common practice at many service facilities.
Although these balancing methods can reduce vibration when the vehicle is lifted off of the ground, they do not entirely eliminate vibrations occurring during on-road performance. Actual driving conditions present additional first order vibrations or change existing first order vibrations. One of the most significant sources of these additional vibrations is that of the loaded, rolling tire. The loaded, rolling operation of a tire introduces excitation and response dynamics that are relatively large and not accounted for in either of the balancing methods described previously. Accordingly, the first order vibrations generated with the vehicle in motion are significantly different than the first order vibrations generated by the independent wheel off the ground. Therefore these vibrations are not compensated for by conventional off-ground balancing techniques.
The present invention provides an on-road balancing system that is responsive to rotational input from a vehicle wheel and vibration sensed on any part of a vehicle to reduce or eliminate vibrations occurring on that part.
In a first aspect of the invention, an on-road balancing system is provided that includes an analyzer, vibration sensor, and rotation sensor. The rotation sensor is coupled to at least one vehicle wheel and the vibration sensor is coupled to a part within the vehicle. The analyzer is responsive to input from the rotation sensor and the vibration sensor to calculate a measurement representative of vibrations transmitted from the wheel to the part. In another aspect, a vehicle is provided having the on-road balancing system as described above.
In a further aspect of the present invention, four rotation sensors are coupled to four respective wheels of the vehicle. The analyzer is responsive to input from each of the four rotation sensors and the vibration sensor to calculate a measurement representative of each wheel""s vibration contribution.
In another aspect, a method for conducting on-road balancing of vehicle wheels is provided. Here, a vibration sensor is placed on a part of the vehicle and a rotational sensor is coupled to a vehicle wheel. Base vibration and rotational data are recorded from the sensors. With this information, a base measurement is calculated. Known weight is placed on the vehicle wheel, and a second set of vibration and rotational data is then taken. An offset is then calculated with the base measurement and the second set of data. An offset weight and location can then be calculated therefrom.